This invention relates to electrostatic copiers in general, and to a developing device for such copiers in particular.
Electrostatic copiers operate on the principle of forming on a surface of an image carrier a latent image--composed of electric charges--of an original to be copied. Thereafter, the latent image is "developed" by adhering toner particles to the charged portions of this latent image to form a visible image, which is then transferred to and fixed as a copy carrier, e.g., a sheet of copy paper. This is a simplified explanation, but it suffices to point out the need for the presence of a developing device in such copiers. It is these developing devices which furnish and meter the required toner.
Devices of this type are known which have a toner-feeding spiral whose purpose it is to feed toner and to discharge it over a relatively small area. These devices are usually employed for returning into circulation such quantities of residual toner as have been recovered in a cleaning station. However--and this will be more fully explained later herein--such devices are also suitable for furnishing (feeding) toner from a supply bottle that can be connected to the copying machine.
A problem, resulting from the small toner discharge area of these devices, is the difficulty which is experienced in mixing-together of the toner. One proposal for a remedy has been made in German Published Application No. 2,551,985. This described a relatively complicated cross-mixer which causes forced mixing of the toner-carrier particle mixture. Due, however, to this forced mixing a high rate of toner-carrier mixture wear is experienced with this equipment, so that the mixture must be frequently replaced for adequate copying results.
A simpler cross-mixer, and one which exerts much less wear on the toner-carrier mixture, is disclosed in German Published Application No. 2,161,835. This equipment is not, however, suitable for the rapid distribution of a toner component that has been admitted into the developing device at a certain location thereof.